Dr Squirrell carried out the research as part of his professional doctorate at Melbourne's Swinburne University.

Of the people who completed the questionnaire, 55 per cent said they were either married or in a serious offline relationship.

"I suppose one of the problems with it is that when you engage in cyber sex frequently enough, the actual arousal pattern to your partner often diminishes and it actually gets replaced with the online images," Dr Squirrell said.

"There's lots of people who report they actually prefer engaging in cyber sex and looking at pornography and masturbating online than actual face-to-face-encounters."

Mr Squirrell says online infidelity can have the same impact on a partner as other forms of cheating.

"Even if somebody isn't actually meeting up with somebody online it has the same sorts of ramifications as a face-to-face affair, because people feel that they've been cheated on even if the partner's just looking at pictures," he said.

Dr Squirrell's survey shows men have a strong preference for looking at pornographic pictures and videos, while women are twice as likely to use web cameras, to send sexually explicit emails or spend time in chat rooms.

He recruited survey participants by advertising within cyber sex user groups - sites that are generally used by people who spend a greater than average amount of time engaged in cyber sexual activities.

Almost half of those who took part in the survey live in North America; 12 per cent said they were Australians.

The average respondent was male, well-educated, and in their early 40s.

Around 40 per cent of respondents identified themselves as heterosexual, with others listing their sexual orientation as gay, lesbian or bi-sexual.

Hours of online sex

While the average participant in Mr Squirrell's sample group said they spent just over 12 hours a week engaging in sexual activity online, some people reported engaging in cyber sex for up to 10 hours a day.

Dr Squirrell says while not all sexual activity online is harmful, some people are desperate to overcome an addiction to online sex.

He treats about seven online sex addicts at his practice in Melbourne's inner south.

"They're absolutely at the end of their tether in terms of being able to control their behaviour themself," he said.

"Clients will even go as far as putting filters and blocks on websites. They've often made changes like putting their computer into other rooms.

'I've got one client who frequently looks at cyber sex at work and just struggles to control that behaviour."

Fighting the addiction

Dr Squirrell says he often suggests people fighting an addiction to cyber sex install filtering devices or join support groups such as Sex Addicts Anonymous, which offer a 12-step program based on the Alcoholics Anonymous model.

He says it is important to realise that not all cyber sexual activity is harmful.

"Most people can engage in cyber sex and take it or leave it. But there is significant minority, like there is with all addictions, where the behaviour just gets absolutely completely out of control," he said.

Dr Squirrell says there is a need for more support services for people who do want to overcome their online sex addiction.

"There's very few people out there who really specialise in the area," he said.

"What I'm trying to get off the ground is actually an e-therapy program like they have for some other conditions, with training modules where people can actually go through the process of treatment online and engage with a therapist occasionally.